Statistical analysis of electromigration (EM) lifetimes of inlaid copper interconnects, in situ microscopy experiments at embedded inlaid copper interconnect structures, and numerical simulations of grain growth and EM degradation processes are necessary for future on-chip interconnect systems with high immunity to EM-induced failure. Experimental results, i.e., statistics of lifetime and void distributions, copper microstructure data from electron backscatter diffraction studies, as well as in situ scanning electron microscopy and transmission X-ray microscopy studies of EM degradation processes, are discussed for inlaid interconnect structures, varying geometry and process conditions. EM failure statistics for a large number of interconnects and in situ studies for a selected number of samples, which allow to visualize the time-dependent evolution of voids, demonstrate that interconnect degradation and, eventually, interconnect failure depend on interface bonding and the copper microstructure. With decreasing interconnect dimensions, the copper microstructure will become more critical for interconnect reliability.

With the introduction of 65 nm technology, the cross-sectional dimensions of copper interconnect in some layers are now smaller than 100 nm, which translates to current densities on the order of several MA/cm2. Electromigration as a root cause for chip failure is thus a major concern and is still being examined. In this article, the authors present recent failure analysis studies on metal-coated copper interconnects, using OBIRCH techniques in combination with FIB cross-sectioning and SEM and TEM imaging.

For successfully developing and controlling BEoL structures of the 32 nm CMOS technology node and beyond, advanced analytical techniques are needed for process development and control, for physical failure localization and analysis as well as for the investigation of reliability-limiting degradation mechanisms. These challenges are discussed from the point of view of a high volume leading-edge manufacturing.

In‐situ SEM electromigration studies were performed at fully embedded via/line interconnect structures to visualize the time‐dependent void evolution in inlaid copper interconnects with additional CoWP coating. Void formation, growth and movement, and consequently interconnect degradation are changed compared to the process of record. The degradation dynamics depends on both, interface bonding and copper microstructure. The increased bonding strength of the top interface of the copper interconnect line reduces the electromigration‐induced mass transport along the interfaces significantly. As a consequence, grain boundary diffusion and liner interface diffusion becomes increasingly important for electromigration‐induced degradation processes.

Abstract In this paper an experimental set-up is presented that allows the Scanning Electron Microscope (SEM) in-situ investigation of electromigration phenomena in fully embedded copper interconnect structures, both from a top-down and from a cross-sectional perspective. The condition that the interconnects under test are fully embedded during the in-situ experiment is achieved using a Focussed Ion Beam (FIB) preparation technique. A SEM is equipped with a custom-made heating stage. During the experiment the void formation, growth and agglomeration process can be observed. Post-mortem cross-section analysis after the interconnect failure reveals e.g. a relationship between the microstructure of the copper contact and the non-constant growth rate of the voids.

An experimental set-up is presented, that allows in situ scanning electron microscope (SEM) investigations of the progress of electromigration damage in fully embedded copper interconnect structures. A LEO Gemini 1550 SEM has been equipped with a heating stage and electrical connections for the experiment. The studied interconnect structures are usually used for reliability testing in electromigration ovens. These test structures are located within the scribelines of wafers. Therefore, they allow the characterization of the electromigration behaviour of products on the wafer. To enable the SEM observation, focused ion beam (FIB) was used to prepare cross-sections of the samples maintaining their electrical functionality. Thereby, a thin layer of passivation was left over in front of the interconnects to keep them fully embedded. The SEM images which were taken at an angle of 60° allow the observation of both the entire via/contact and the connecting lines. Multiple images were recorded during the degradation experiments. The resulting video sequences provide a good visualization of the formation, growth and motion of voids at the stressed interconnects. The dominant diffusion path has been identified.